1. Field of the Invention
The invention relates to a start system and a start control method for an internal combustion engine of a hybrid vehicle.
2. Description of Related Art
As a controller that is applied to a hybrid vehicle that is equipped with an automatic transmission gear device, a controller is known that changes the transmission gear ratio of the automatic transmission gear device before starting the internal combustion engine when there is a request to start the internal combustion engine (Japanese Patent Application Publication No. 2013-159260 (JP 2013-159260 A)). As another related art document that relates to the invention, there is Japanese Patent Application Publication No. 2013-35528 (JP 2013-35528 A).
Usually, in a hybrid vehicle, the engine speed and engine torque are determined so that the internal combustion engine can be operated in an optimum fuel efficiency condition. However, when the internal combustion engine is started in an optimum fuel efficiency condition when it has not been warmed up, the emission may be deteriorated. In particular, it is known that, in this situation, the number of particulate matters (PN: particulate number) increases.
To avoid such deterioration of emission, the controller of JP 2013-159260 A changes the gear position of the automatic transmission gear device to a low-speed side (engine high-speed side) before starting the internal combustion engine and returns the gear position of the automatic transmission gear device to the original gear position after the completion of warm-up of the internal combustion engine. This helps to prevent a decrease in transmission efficiency of the automatic transmission gear device. For example, when the gear position is changed from the second gear to the first gear in starting of the internal combustion engine, the gear position is changed from the second gear to the first gear and then to the second gear. When the period from start-up of the internal combustion engine to the completion of its warm-up is short, the gear position may be changed at frequent intervals and the user feels uncomfortable.